1. Field of the Invention
This invention relates to liquid treatment and more particularly to controlling the flow of particle-laden water to promote particle settlement in water and waste water clarification systems.
2. Description of the Prior Art
Clarifiers are used to remove certain materials or particles from liquid. These materials are generally suspended in the liquid and can be removed under the force of gravity when the flow of the liquid is substantially reduced, as in a very low flow, or quiescent, zone in the clarifier. Since these materials are generally solid and are said to "settle" out of the liquid, they are referred to as "settleable solids". Such settleable solids may include naturally occurring materials (e.g., clay, silts, sand and dirt), chemical precipitants and biological solids. The word "solids" as used herein to describe the present invention refers to such settleable solids.
Clarifiers are used, for example, in water and waste water treatment plants. In water treatment, the water drawn from a water supply has various non-settleable colloidal solids therein. When mixed with chemicals, the colloidal solids and chemicals agglomerate to form solids. In waste water treatment, the solids include organic solids, among other wastes. Water and waste water are treated in clarifiers to remove such solids, thereby making the water clear and suitable for use, reuse, or for further treatment, such as tertiary treatment. The word "liquid" as used herein to describe the present invention refers to water and waste water.
An object of water and waste water clarifiers is to create quiescent zones having very low flow rates to promote maximum settlement of solids to the bottom of the clarifiers. Clarifiers typically include a large detention basin where the settlement of the solids occurs. Tubes or flat sheets mounted at fixed angles relative to the surface of the liquid have been used to form multiple thin liquid flow paths and create quiescent zones within the detention basin in an attempt to promote settling of solids. Plates have also been mounted within detention basins at fixed angles relative to the surface of the liquid. To date, such plates have been constructed out of relatively heavy, single sheets of metal or plastic that are supported on their sides and connected to the sidewalls of self-contained modules positioned within detention basins. The liquid containing the solids flows upwardly between the plates or tubes at flow rates that generally allow sufficient time for most of the solids to settle onto the plates or tubes. Ideally, the solids then slide down the plates or tubes to the bottom of the detention basin for collection. Clarified liquid flows out of the openings between and at the top of the plates or tubes.
Prior art clarifiers have also included some type of weir or trough extending across, or along the sides of, the detention basins. Such weirs or troughs are effective to form a relatively thick (e.g., two feet) layer of partially clarified liquid on top of the plates or tubes. The weight of such weirs or troughs necessitates additional support within or surrounding the detention basin, adding to the weight and expense of the clarifiers. In general, the liquid flowing from the tubes or plates into this thick layer is subject to changes in flow rate due to random variations in the upward flow of the liquid through different ones of the quiescent zones of the clarifier. This thick layer is used to diffuse the flow of the liquid from the quiescent zones to the weirs, rendering the flow of the liquid more uniform as the liquid enters the weirs that are at the perimeter of the basin or that extend across the basin.